4 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
cerning my limitation of the Cape region, I will answer that for the 
flora it seems best to include only the region south of a line between La 
Paz and Todos Santos. This line is nearly a straight line, and follows 
along the northern base of the Cape Mountains. The trail between La 
Paz and Todos Santos does not appear to ascend more than 150 feet 
above sea-level at any place, and there is a large extent of nearly level 
country to the north of it. The Cape Region will be, then, a mountainous 
country separated from the northern mountains by an extent of low 
land.” 
The depressed and exceedingly arid desert tract above mentioned 
evidently forms nearly as complete a barrier to the northward and south- 
ward extension of plant and animal life as would a similar expanse of 
ocean. Indeed, there can be little doubt that the comparative isolation 
which its presence affords to the region lying to the southward has had 
very much to do with the striking faunal and floral characteristics of 
the latter area. Another factor of perhaps almost equal potency is the 
comparatively humid climate of the Cape Region with the resultant (but 
also only comparative) luxuriance of its vegetation. 
The limitations so concisely yet clearly stated by Mr. Brandegee are 
those which [ have adopted in the present paper, but I have ventured 
to construe these (wholly without his knowledge or sanction) as includ- 
ing the island of Espiritu Santo, whose fauna, judging by what little we 
know of it, seems to be essentially similar to that of the region lying 
about and to the southward of La Paz. 
It was my original intention to insert in this connection some general- 
izations bearing on the characteristics and affinities of the fauna and 
flora of the Cape Region, as well as to tabulate the names of its various 
birds in lists of permanent residents, summer residents, winter residents, 
migratory visitors, etc., but I have found so very many cases where all 
the information at my command has proved insufficient to enable me to 
reach definite conclusions, that I have become convinced that the time 
has not as yet arrived when it is either safe or profitable to attempt any- 
thing of the kind just indicated ; I may venture to say in passing, how- 
ever, that, as Professor Baird pointed out in 1859, the characteristic 
birds of the Cape Region appear to be more closely related to those of 
Arizona and Northwestern Mexico than to those of California, although 
certain recent developments have shown that this rule is not wholly 
without exceptions. 
